1. Field of the Invention
The present invention relates to sound generating devices, and more particularly to electrically driven bells which may be adjusted in intensity and frequency.
2. Description of the Prior Art
Electrically powered bells have been known in the past, most frequently taking the form of a make and break contact arrangement which is determined in strength and in frequency by the spring mass characteristics of the hammer. In applications where the intensity or the frequency are to be adjusted most of the prior art ringing devices entail elaborate mechanical manipulations which at best are merely repetitive in producing the desired result in a particular installation.
In certain situations, i.e., in installations of fire alarms or other alarm systems, the sound propagation and acoustics of the area monitored exhibit unique and varying patterns with the result that an alarm sized and resonating at one particular frequency will be inappropriate when it is installed. Typically alarms associated with smoke detectors are installed in narrow corridors of a residence which communicates with the bedrooms. Corridors of this size normally exhibit reflection and sometimes cancellation patterns which can only be accommodated by changes in frequency or amplitude. Heretofore the prior art alarm systems lacked the requisite adaptability to the varying room sizes and it is for this reason that control over frequency and amplitude is widely sought.